Coextrusion apparatus

ABSTRACT

A coextrusion head for producing a generally tubular elastomeric ply made up of first and second concentric tubular streams of elastomeric material having interposed, adjacent to their interface, a closely spaced array of parallel reinforcing elements wherein the coextrusion head includes a reinforcing element guide subassembly including a generally annular guide element as well as a mechanism for individually and independently directing and accurately positioning a circular array of uniformly spaced individual reinforcing elements. A generally annular inner die assembly cooperates with the annular guide element to form a first distribution channel and a generally annular outer die assembly also cooperates with the annular guide element to form a second distribution channel, with the guide element cooperating with the inner and outer die assemblies to produce concentric first and second tubular extrudate paths which thereafter merge into a third such path with the individual reinforcing elements being introduced into the interface between the first and second tubular streams of elastic material as they merge into a third tubular stream so as to produce the tubular elastomeric reinforced ply. A method for coextruding an annular seamless component of reinforced elastomeric material is also presented.

TECHNICAL FIELD

The field of art to which this invention pertains is that of acoextrusion apparatus and method, particularly for use in manufacturingannular seamless components of reinforced elastomeric material. Sucharticles, in the form of tubular elements or strips are useful in theproduction of a myriad of products, such as, for example pneumatictires, specifically, body plies for radial tires.

BACKGROUND OF THE ART

Tubular components or articles, such as pneumatic tire body plies havepreviously generally been built by utilizing woven fabric andcalendering same with rubber stock which, when cut to size, entailswrapping the sheet component around a tire building drum and overlappingthe ends of the sheet to produce an annulus with a generally axiallyextending seam. Such a seam is generally disadvantageous in that thediscontinuity in the now annular component may produce not only weakspots, but also an asymmetrical construction tending to cause a forceunbalance in the completed tire.

In order to avoid this lapped or seamed construction, extrusion has beenemployed in the prior art in the case of knit tubular fabric and annularseamless elastomeric tubes having reinforcement cords therein disposedgenerally longitudinally of the tube during extrusion. However, theseattempts have not been commercially successful since there wasinsufficient control in terms of the placement and spacing of the cordsto obtain the desired high performance required in modern engineeredconstructions.

The prior art has not successfully addressed a coextrusion apparatus andmethod to produce an article having a circular array of small diametercords of a very large number (500-2,500) cords in a thin walled (0.070inches) annular tubing ranging up to 16 inches or more in diameter. Intire construction, for example, the uniformity of spacing of thereinforcing cords of the body ply is crucial to the subsequent tirebuilding steps, and uniformity of expansion is a direct result ofuniform spacing of the reinforcement cords.

U.S. Pat. Nos. 2,874,411 and 3,183,135, both to Berquist, disclose anapparatus and method, respectively, for manufacturing a tire. FIG. 4 ofthe former discloses individual strands, from a bank of spools, passinginto an annular guiding aperture of a die head and passing out throughan annular aperture in an exit sleeve. A mandrel supports the strandsand causes the plastic, supplied by a single extruder, to form a tubularstructure in which the strands are parallel. A floating mandrel isutilized and seeks its own location in the outlet and center of thetubular structure so as to prevent the tube from collapsing under thepressure of the plastic. The method of U.S. Pat. No. 3,183,135 includesforming a hollow circumferentially endless cylinder by extrudingparallel strands, substantially longitudinal of a floating mandrel,while simultaneously coating and bridging the strands with an adhesiveinsulating coating, using the apparatus of U.S. Pat. No. 2,874,411.

U.S. Pat. No. 3,615,987 to Blatz is directed to a method of extrudingcontinuous annular seamless components of rubber material, containingreinforcement filaments embedded therein, comprising the steps ofextruding a tube of this material, cutting the extruded tube intopredetermined lengths, and positioning the lengths onto a tire buildingdrum. The extrusion apparatus includes an extrusion head having a nozzlemounted partly within the outlet of the extrusion head so that theinterior surfaces of the nozzle and the extrusion head together form asmooth frustoconical surface which diverges in the direction of the flowof the material being extruded. A conical form core, disposed within theextrusion head outlet portion and the nozzle, is axially movabletherein, thus causing gradual consolidation of the extruded material. Aplurality of substantially radially extending ceramic inserts isarranged on the periphery of the nozzle and communicates with thepassage between the core and the nozzle, with these inserts serving asthe inlets for the reinforcing cords. However, the cords are forced toundergo a 90° transition upon entering the single annular streamextrudate.

U.S. Pat. No. 4,283,241 to Hollmann discloses a method and apparatus forpreparing carcass plies for radial tires wherein the apparatus includesextruding means including a plurality of nozzles for separatelyextruding, from each nozzle, a strand of vulcanizable rubbercomposition, wherein the nozzles are arranged to extrude a plurality ofstrands in a tubular array. Elongated reinforcing members are fed to thenozzles respectively for discharging therefrom respective reinforcingmembers individually coated with the rubber composition. However,textile machinery means are utilized for winding the coated strands withrelatively weak transfer circumferential strands. It appears that but asingle extruder is utilized.

U.S. Pat. No. 4,484,966 to Kawamoto discloses a process of manufacturingcarcass bands which are reinforced by cords and are employed infabricating a radial tire. This process includes the steps of unwindingthe plurality of cords from a plurality of reels, traveling the cordsthrough apertures formed in guide members and entering a rubber coatingmechanism and thereafter coating the cords with rubber material by meansof the rubber coating mechanism to produce a continuous cylindrical tubehaving cords embedded therein. A pair of controlled rollers, upstreamfrom the coating mechanism, is utilized for maintaining the cords evenin tension and to prevent their twisting. A plurality of guide members,immediately upstream of the coating mechanism, guides the cords prior toentering the passageways within the rubber coating mechanism. Again,only a single hollow stream of elastomeric material is utilized.

U.S. Pat. No. 4,050,867 to Ferrentino et al. discloses an extrusion headfor extruding elastomeric material on at least two filaments having adiameter on the order of 0.1 mm and having a high modulus of elasticitywhile maintaining a constant spacing therebetween. The nature of thecord guides illustrated in the patent is not adequate to control a largenumber of textile cords and prevent entanglement. U.S. Pat. No.4,132,756, also to Ferrentino et al. and a division of U.S. Pat. No.4,050,867, is cited for its disclosure of an extrusion process whereinthe five filaments (F and W) are subjected to mechanical tension appliedfrom the outside of the extrusion head in any conventional manner,thereby providing a cable with a constant spacing between the filaments.

U.S. Pat. No. 4,150,929 to Brandt pertains to the preparation ofminiature ribbon cables having up to 100 fine conductor wires of adiameter of 0.010 to 0.015 inches. The gauge of the extrudate of thepresent invention must be controlled within a few mils whereas theadjustment of the die position of Brandt, via rocking set screws 53 and54, is inadequate to control the gage over the large circumferentialdimension characteristic of the present composite tire component. WhileBrandt's quills 37 are formed of thin-walled material, such ashypodermic needle stock, their delivery ends are swaged down to reducethe internal diameter to a dimension close to the external diameter ofthe wires. Swaged ends, as those in Brandt, would require replacement ifelastomeric material backs into the flow tube should a cord break. Inthe apparatus of the present invention, not only is the backflow slight,but if a reinforcing element break is detected while running,rethreading can even be accomplished under operating conditions.

U.S. Pat. No. 3,697,209 to Schiesser discloses an apparatus formanufacturing reinforced tubings from plastic materials wherein a firstinner layer of the tubing wall is continuously extruded, in an extruderhead, over a guide serving to form the cavity of the tubing whereinafterstrand-like reinforcing material is continuously applied in alongitudinal direction of the tubing on the outer surface of this innerlayer which is thereafter coated by at least one further or outer layerof a plastic substance. The apparatus and method of Schiesser differ,among other things, from the present invention in that the latterintroduces the reinforcing elements into the interface of two mergingcircumferentially continuous concentric streams.

DISCLOSURE OF THE INVENTION

The present invention provides a solution to the noted prior artproblems in terms of apparatus by producing a generally tubularelastomeric ply made up of first and second concentric tubular streamsof elastomeric material having interposed, adjacent to their commoninterface, a closely and uniformly spaced array of parallel reinforcingelements.

The coextrusion head of the present invention includes a reinforcingelement guide subassembly, including a generally annular guide elementhaving inner and outer wall surfaces, as well as axially-directed meansfor individually and independently directing and accurately positioninga circular array of closely and uniformly spaced individual reinforcingelements. A generally annular inner die assembly, having inner and outerwall surfaces, is concentric with and located substantially radiallyinwardly of the annular guide element, wherein one or both of theannular guide elements and/or the inner die assembly have a 360° annularcontoured channel in their wall surfaces, so that this channel, togetherwith its opposed wall surface, forms a first distribution channel. Agenerally outer die assembly, having inner and outer wall surfaces, isconcentric and located substantially radially outwardly of the annularguide element, wherein one or both of the annular guide and/or the outerdie assembly have a 360° annular channel in one of its wall surfaces, sothat this channel together with its opposed wall surface, forms a seconddistribution channel.

The axial outer portions of the inner and outer wall surfaces of theannular guide element have converging portions that merge into an endportion having a narrow annular outer end surface. A portion of theinner die assembly outer wall surface and a portion of the annular guideelement inner wall surface, both axially outward of the firstdistribution channel, cooperate to form a first generally tubularextrudate path. A portion of the annular guide element outer wallsurface and a portion of the outer die assembly inner wall surface, bothaxially outward of the second distribution channel, cooperate to form asecond generally tubular extrudate path.

The axially outermost portions of the inner wall surface of the outerdie assembly and the outer wall surface of the inner die assembly alsocooperate to form a third generally tubular extrudate path with thefirst and second extrudate paths merging together into this third pathat the narrow annular end surface of the guide element.

First and second inlet streams of elastomeric material enter the firstand second distribution channels and consequently the first and secondannular tubular extrudate paths, respectively produce first and secondtubular outlet streams which thereafter merge together into a thirdtubular outlet stream of elastomeric material in the third extrudatepath, with individual reinforcing elements being introduced into theinterface between the first and second outlet streams as they mergetogether into the third such stream to produce the tubular elastomericply that is internally reinforced with a closely and uniformly spacedarray of parallel reinforcing elements.

The means for individually and independently directing and accuratelypositioning the individual reinforcing elements preferably take the formof at least one spaced array of adjacent thin walled, deformable,semi-rigid tubes, preferably of metallic construction. The narrow,annular outer end face of the annular guide element is coplanar with theaxial outer end surfaces of the tubes, with the inlet portions of thetubes being flared in order to prevent chafing of the reinforcingelements.

In a preferred embodiment of the present invention, both the inner dieassembly and the guide subassembly each have a 360° annular contouredchannel in their outer wall surfaces, these channels together with theiropposing wall surfaces forming the first and second distributionchannels, respectively.

The reinforcing element guide subassembly includes a back plate, withfirst and second means mounted on the back plate and operativelyinterconnected with the inner and outer die assemblies, respectively,for independently translating the inner and outer die assemblies and thereinforcing element guide subassembly relative to one another.

A method of coextruding an annular seamless component of reinforcedelastomeric material comprises the steps of producing a first annularhollow stream of elastomeric materials; producing a second annularhollow stream of elastomeric materials; producing a third annular hollowstream of elastomeric material from the first and second streams,wherein the third stream includes a common, annular merger interfacebetween the first and second streams; and interposing, into the thirdstream at this interface, a closely spaced annular array of reinforcingelements parallel to the longitudinal axis of the third stream. Tubularcomponents, such as tire body plies can be produced by circumferentiallysevering the annular seamless component into predetermined lengths.Sheets or strips can be produced by longitudinally severing the annularseamless component.

In a preferred embodiment of the present invention, the producing of thefirst and second annular outlet streams is initiated with the first andsecond extruders, respectively. In addition, the producing of the thirdannular outlet stream is accomplished by merging the first and secondoutlet streams within a coextrusion head, with these first and secondstreams being coaxial and preferably, if circular in cross section,concentric. The interposing step includes initially directing thereinforcing elements, in the coextrusion head, to the merger interface,with the directing step including independently and individually totallyenveloping each of the reinforcing elements. The interposing stepfurther includes utilizing the movement of the streams for drawing thereinforcing elements into the interface of the streams.

The method of using the apparatus of the present invention also includesthe producing of each of the first and second annular hollow outletstreams by delivering inlet streams of elastomeric material, fromseparate extruders, via separate openings, perpendicularly into thecoextrusion head; splitting each of the inlet streams into equalportions; and flowing these equal portions through annular contouredchannels for achieving annular outlet streams having a uniform 360°distribution of elastomeric material and a circumferentially uniformexit velocity as well as wall thickness.

The exit velocities of each of the outlet streams is substantiallysimilar, with the pressures of the inlet streams, as delivered into thecoextrusion head, being in the range of about 2,500-5,000 psi, whereasthe pressures of the outlet streams, at their ahnular merger interface,drop to a range of about 500-700 psi.

Other features and advantages of the present invention will become morereadily understood by persons skilled in the art when following the bestmode description in conjunction with the several drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the coextrusion head of the presentinvention.

FIG. 2 is a front elevational view of the exit end of the coextrusionhead.

FIG. 3 is a rear elevational view of the reinforcing element entranceend of the coextrusion head.

FIG. 4 is a horizontal sectional view, in a longitudinal direction takenalong lines 4--4 in FIG. 3 wherein the head is in its closed position,with the outer distribution channel being shown in elevation.

FIG. 5 is a horizontal sectional view, substantially similar to that ofFIG. 4, but with the inner distribution channel being shown inelevation.

FIG. 6 is a horizontal sectional view, similar to that of FIGS. 4 and 5,with the inner die assembly being shown in its open position.

FIG. 7 is a horizontal sectional view, similar to that of FIG. 6, butwith the outer die assembly being shown in its open position.

FIG. 8 is an enlarged fragmentary view of the exit end of the die orextrusion device which shows the reinforcing element guide membermounting within the guide subassembly as well as the extrudate path.

FIG. 9 is an enlarged fragmentary view taken at the entry end of thecoextrusion head showing the reinforcing element entrance area.

FIG. 10 is an enlarged fragmentary elevational view of one of the slotsat the entrance and of the coextrusion head shown in FIG. 3.

FIG. 11 is an enlarged fragmentary view taken on lines 11--11 of FIG. 8,which shows the position of the array of guide members near the exit endof the coextrusion head.

FIG. 12 is an enlarged fragmentary view taken on lines 12--12 of FIG. 8and showing the cross-section through the coextruded reinforcedelastomeric ply.

FIG. 13 is an enlarged fragmentary elevational view taken on lines13--13 of FIG. 6, which shows the center flow divider on the inner flowchannel.

FIG. 14 is an enlarged fragmentary section taken on lines 14--14 of FIG.6 which also shows the flow divider on the inner flow channel.

FIG. 15 is an enlarged sectional view taken on lines 15--15 of FIG. 7and shows the entry to the inner flow channel through the reinforcingelement guide subassembly as well as the flow dividers on both of theinner and outer flow channels.

FIG. 16 is an enlarged elevational fragmentary view taken on lines16--16 of FIG. 15 and shows the guide members routed around theextrudate opening to the inner flow channel together with the locatinggrooves near the exit end of the coextrusion head, namely on the innermember of the reinforcing element guide subassembly.

FIG. 17 is an enlarged elevational fragmentary view taken on lines17--17 of FIG. 15 and shows one of the spacing ribs between the innerand outer members of the reinforcing element guide subassembly togetherwith the locating grooves, near the exit end of the coextrusion head, onthe inner member of the reinforcing guide subassembly.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, specifically to FIG. 1, there isillustrated a top plan view of the coextrusion head generallydenominated by the numeral 20, of the present invention. Coextrusionhead 20 is comprised of three main elements; namely, reinforcing elementguide subassembly 22, (best shown in FIGS. 4 and 6), inner die assembly24 (best shown in FIGS. 5 and 6) and outer die assembly 26 (best shownin FIG. 7), all of which will be discussed in more detail hereinafter.Coextrusion head 20 is utilized to produce a tubular elastomeric plybest shown in FIGS. 8 and 12.

Reinforcing element guide subassembly 22, as best seen in FIGS. 4 and 6,includes a back or support plate 30 whose lower portion 32 (FIG. 2) maybe provided with a base portion (not shown) for the support thereofrelative to any desired type of substrate, be it vertical, horizontal orangulated therebetween. As best seen in FIGS. 4 and 6, reinforcingelement guide subassembly 22 includes a generally annular guide element34 whose inner axial end surface 36 is physically located on and rigidlyattached to back plate front surface 38 by a plurality ofcircumferentially spaced bolts 40. Inner wall surface 42 (FIG. 6) ofguide element 34 is preferably outwardly tapered for reasons to bedescribed hereinafter, while its outer wall surface 44 is preferablycylindrical. As best seen in FIG. 8, the axial outer end portions 46 and48 of wall surfaces 42 and 44 respectively, converge to form an annulartapered end portion 50, being a solid of revolution, having a generallytrapezoidal outline (not shown per se) in full transverse section, orbeing of a generally trapezoidal shape (FIG. 8) in radial section.Portion 50 has an included angle, between surfaces 46 and 48, rangingfrom about 30° to about 180°, but is preferably in the 100°-120° rangeand has a narrow annular end surface 52 which is perpendicular to theaxial extent of guide element 34.

For ease of manufacture, annular guide element 34 is preferably made upof concentric inner and outer press or interference-fitted annularportions 56, 58 that are spaced from one another via a plurality ofintermediate spacing ribs 60 in the manner best shown in FIGS. 15-17,thus producing a plurality of circumferentially-spaced arcuate axialopenings 64 between annular portions 56 and 58. Spacing or locating ribs60, which maintain concentricity between inner and outer annular guideelement portions 56, 58 respectively, have their forward or innerportions 68, tapering together to a point in a manner best shown inFIGS. 16 and 17. In addition, the axial extent of tapered portions 68stops prior to reaching annular tapered end portion 50 thus permittingan annular circumferential space 70 best seen in FIG. 11, to existbetween guide element portions 56 and 58. In addition, in the area ofguide element tapered end portion 50, inner annular portion 56 isprovided with a cirbumferentially arranged, axially directed, series ofspaced serrations or notches 72 (best seen in FIGS. 8, 11, 16 and 17).

The innermost ends of arcuate axial openings 64, i.e. those adjacent toback plate front surface 38, are aligned with corresponding pluralitiesof circumferentially spaced arcuate openings 66 extending through backplate 30 as best seen in FIGS. 3 and 9.

As will be described in more detail later, the elongated,circumferentially continuous preferably tubular, elastomeric body or ply28 produced via the use of coextrusion head 20 incorporates one or moreclosely-spaced large orderly groupings or arrays of parallel reinforcingelements 80, best seen in FIG. 12, which generally take the form offilaments, threads, yarns or cords including, but not limited to,natural or synthetic textiles (cotton, nylon, polyester, rayon, aramidor hybrids thereof), steel wire or fiberglass, etc. A ply is made up ofa plurality of closely spaced reinforcing elements precisely skimmedwherein each element is fully surrounded by elastomeric material. Theterm "ply" may also further be defined as one of a number of layers ofreinforced fabrics used in a tire construction. Reinforcing elements 80,which are shown in FIG. 12 as a staggered array, could of course also bein one or more spaced linear or curvilinear arrays, if so desired. Inorder to direct such a plurality of reinforcing elements intocoextrusion head 20, each reinforcing element is separately andindependently guided into and at least partially through coextrusionhead 20 via one or more of closely-spaced arrays of adjacent guide means82 that take the form of thin-walled, deformable, semi-rigid conformabletubes, preferably of metallic composition, which direct and accuratelyposition the circular array of individual reinforcing elements 80. Guidemeans 82 are axially directed through back plate openings 66 and guideelement openings 64, around spacing ribs 60, into annularcircumferential space 70, with the guide means axial outlet end faces 84being coplanar with guide element narrow annular end surface 52 (seeFIG. 8). As best seen in FIG. 11, the arrays of guide means 82 arereceived either in serrations 72 or between each other and are thusuniformly spaced around the entire 360° extent of annular space 70.Preferably guide means 82 are replacably secured in annular space 70 viacurable adhesive, soldering or brazing (not shown), etc. Guide means 82may be arranged in one or more linear or staggered arrays. Naturally,their placement is limited by the outside diameters of the individualtubes. As best seen in FIG. 9, guide means axial inlet portions 86 areflared in order to prevent the chafing of reinforcing elements 80.

Annular guide element 34 is also provided with a transverse bore oraperture 90, which bore extends through one of the spacing ribs 60 (FIG.16) in order to convey elastomeric material through the guide array. Inaddition, guide element outer annular portion 58 is also provided with a360° annular contoured channel 92 of varying cross section, with channel92 being made up of two substantially similar and angularly directed180° portions 92a, 92b which emanate from an axial flow divider 94 (FIG.15) which in turn is preferably located in the same plane containing theaxis of coextrusion head 20, but 180° removed from aperture 90.

Another of the main elements of coextrusion head 20 is inner annular dieassembly 24, best seen in FIG. 6, which is preferably made up of aninner cylindrical portion 100 which is physically secured to outer,generally tapered or frustoconical, portion 102. The interface 104between inner and outer portions 100, 102 respectively, is provided witha temperature control means, which preferably takes the form of channels106 that may be used for circulating fluid for temperature controlpurposes in a manner well known in the art. The rear end of annularportion 100 is provided with a stepped annular cap member 110 which inturn is provided with a threaded central aperture 112. The axial outerend face of assembly 24 is provided with an annular outer end face 120.The axial inner end face 114 of outer annular portion 102 is providedwith a plurality of circumferentially spaced threaded blind holes 116which are angularly aligned with similar pluralities of apertures 76 inback plate 30 thus permitting the attachment of inner die assembly 24 toback plate 30 via pluralities of bolts 118.

Attached to rear surface 54 of back plate 30 is a dual acting fluidpressure operated piston cylinder apparatus 122 whose threaded distalpiston rod end 124, extending through back plate aperture 62, isphysically secured in threaded cap member aperture 112, so that upon theremoval of bolts 118, piston-cylinder apparatus 122 can translate innerdie assembly 24 and back plate 30 relative to one another.

The outer wall surface 128 of inner die outer annular portion 102 istapered outwardly, starting from axial rear end face 114 and is providedwith a circumferential first or rear land portion 130 and a second orintermediate contoured peripheral land portion 132, which are adapted tomate with and be seated on inner wall surface 42 of annular guideelement 34 so as to concentrically and sealingly position inner dieassembly 24 relative to reinforcing guide subassembly 22. Inner dieouter portion 102 is also provided, on its outer wall surface 128, witha 360° annular contoured channel 136 of varying cross section, withchannel 136 being made up of two 180° portions 136a, 136b emanating froman axial flow divider 140 (FIGS. 13, 15 and 16), with flow divider 140essentially bisecting the radial inner end of aperture 90. It shouldalso be noted that land area or portion 132 follows the contour ofchannel 136 at its rearward or inner end, as best seen in FIG. 13.

Inner die outer wall surface 128 is also provided, toward its axiallyoutermost portion with a tapered or contoured portion 144 which mergesinto a further substantially cylindrical portion 146 that forms theaxially outermost portion of inner die assembly 24. Contoured portion144, on its inner end, merges into that peripheral portion 148 of outerwall surface 128 that is located axially outwardly of channel 136, withland portion 148 acting as a third or outer land portion of wall surface128.

Inner die peripheral wall portion 148 cooperates with element guide wallsurface 42 to define, therebetween, a first generally annular tubularextrudate path 150 (as best seen in FIG. 8). Furthermore, inner die wallcontoured portion 144 cooperates with reinforcing element guide axialouter portion 46 to define annular inner die throat 152 therebetween.

Turning now to outer die assembly 26, best shown in FIG. 7, it includesan outer cylindrical shell 160 and a mating concentric inner cylindricalsleeve 162, with the interface 164 therebetween being provided withtemperature control means, which preferably takes the form of channels166 that may be used for circulating fluids. Matingly located on theinner peripheral surface 168 of cylindrical sleeve 162, adjacent to itsouter end surface, is outer die element 170 whose inner wall surface iscomprised of a tapered or contoured portion 172 that merges smoothlyinto a cylindrical portion 174. The included angle between contouredsurfaces 172 and 144 (FIG. 8), which cooperate to define a generallyinwardly tapered or converging annular shape, can range from about 180°to 40°, but is preferably in the 130°-110° range. Die element 170 alsohas an annular outer end surface 176, with a externally threaded ringmember 180, mating with an internally threaded portion of outer shell160, bearing against end surface 176.

As previously noted, contoured channel 92 (FIGS. 4, 7 and 8) is providedin guide element portion 58, but if desired, channel 92 could also beprovided, with proper redesign, in inner surface 168 of outer diecylindrical sleeve 160. In addition, circumferential portions of channel92 could be provided in both guide element portion 58 and cylindricalsleeve 160. Furthermore, while contoured channel 136 is provided ininner die outer wall surface 128, it could also be provided, with properredesign, in inner surface 42 of annular guide element 34. Further yet,circumferential portions of channel 136 could be provided in both innerdie outer wall surface 128 and guide element inner surface 42.

Outer shell 160 (FIG. 7) of outer die assembly 26 is also provided withtwo oppositely directed and transversely extending rear attachmentportions 182, each having a threaded aperture 184 that serve to receivethe distal threaded ends of piston rods 188 of a pair of dual actingfluid pressure operated piston and cylinder devices 186. These devices,whose piston rods extend through back plate apertures 74 and which arephysically attached to the back plate rear surface 54, are utilized fortranslating reinforcing element guide subassembly 22 and outer dieassembly 26 relative to one another. The axial rear end face 190 ofouter shell 160 is provided with a circumferentially spaced plurality ofthreaded blind holes 192 which are angularly aligned with apertures 78in back plate 30 so that outer die assembly 26 can be rigidly attachedto reinforcing element guide subassembly 22 via bolts 194.

Outer die assembly 26 is also provided with two diametrically opposedthreaded stepped apertures 195, 196 extending through cylindrical shell160 and sleeve 162. Threadably received within apertures 195, 196 arethe proximate ends of delivery conduits 197, 198 respectively, whosedistal ends are connected to the outputs of preferably two seperateextruders (not shown). In the closed condition of coextrusion head 20,as best shown in FIGS. 4 and 5, the angular alignments of reinforcingelement guide subassembly 22, inner die assembly 24 and outer dieassembly 26 are such that outer die element transverse aperture 195 isaligned with annular guide element transverse aperture 90, the latteralso being axially centered relative to axial flow divider 140 of innerdie assembly distribution channel 136. Similarly, as best seen in FIGS.4 and 15, outer die assembly transverse aperture 196 is aligned withdistribution channel 92 of reinforcing guide subassembly 22 in that itsaxial flow divider 94 is essentially axially centered relative toaperture 196.

As best seen in FIGS. 7 and 8, the peripheral or land portion 96, ofouter guide element outer wall surface 44 that is axially outwardly ofdistribution channel 92 cooperates with that portion of the innersurface 168 of outer cylindrical sleeve 162, corresponding to landportion 96, to define therebetween, a second generally tubular extrudatepath 200. Furthermore, outer die wall contoured portion 172 cooperateswith element guide axial outer portion 48 to define annular outer diethroat 202 therebetween.

Again as best seen in FIG. 8, first and second extrudate paths 150 and200 merge together into a third generally tubular extrudate path 204which is defined between outer die cylindrical surface portion 174 andinner die cylindrical surface portion 146.

As best seen in FIG. 5, a first extruder (not shown) delivers a firstsingle inlet stream 206a (FIG. 8) of elastomeric stock via conduit 197,through aligned apertures 195 and 90 into inner or first distributionchannel 136, with central flow divider 140 (FIGS. 13, 14, 15)essentially halving or equally splitting stream 206a so that theportions thereof flow in channel portions 136a, 136b to achieve a 360°distribution, with channel 136 of course cooperating with acorresponding portion of annular element guide inner wall surface 42 soas to define, in total, a covered first distribution channel 136 ofvarying cross section. As best seen in FIG. 13, land area 132 bordersthe rear or inner contours of the channels 136a, 136b whereas the frontcontours of these channels merge into generally annular tubularextrudate path 150 so as to produce first annular tubular or outletstream 206b, as best seen in FIG. 8. Elastomeric stock outlet stream206b, having inner and outer cylindrical surfaces 208, 210,respectively, then proceeds to flow through first extrudate path 150 andinner die throat 152.

In a manner similar to that described hereinabove, a second single inletstream 214a of elastomeric stock (FIG. 8), preferably from a secondextruder (not shown), enters through delivery conduit 198 and aperture196, into 360° annular contoured channel 92, which as previously noted,is made up of two substantially similar and angularly opposite directed180° portions 92a, 92b, which emanate from axial flow divider 96 (FIGS.15, 16). Channels 92a, 92b provide the required 360° distribution ofelastomeric stock stream 214, with stream 214 flowing from channels 92a,92b axially outwardly through second extrudate path 200 so as to producesecond annular tubular or outlet stream 214b, as best seen in FIG. 8.Outlet stream 214b, having inner and outer cylindrical surfaces 216, 218respectively, then proceeds to flow through second extrudate path 200and outer die throat 202.

Again as best seen in FIGS. 8 and 12, first and second outlet streams206b and 214b of elastomeric stock merge together, into third outletstream 224, in the area of narrow annular end surface 52 of annularguide element annular end portion 50. Stream inner surfaces 208 and 216form a coplaner interface or stock junction 220 (schematically shown inFIG. 12) between outlet streams 206b and 214b, respectively.

As its name implies, reinforcing element guide subassembly 22 serves toretain and guide a plurality of reinforcing elements or cords 80. Eachreinforcing element 80 is separately and independently guided intointerface 220 between merging outlet streams 206b and 214b ofelastomeric stock in the area of end face 50 of annular guide element34. As previously noted, this guiding function is provided by one ormore closely-spaced arrays of adjacent guide means 82 as best seen inFIGS. 8-11 and 16. As noted, the axial end surfaces 84 of guide means 82are coplaner with guide element narrow annular end surface 52 and thusserve to precisely locate and feed reinforcing elements 80 intointerface 220, defined by juxtaposed elastomer stock stream innercylindrical surfaces 208 and 216. The resultant force of merging outletstreams 206b and 214b, into third outlet stream 224 (FIG. 8), serves todraw reinforcing elements 80 into and through coextrusion head 20. Thethickness 222 (FIG. 12) of elastomeric body 28, which is comprised ofmerged outlet streams 206b and 214b, having reinforcing elements 80embedded therein, is of course controlled by a third extrudate path 204,i.e., the spacing, throat or orifice between inner die surface 146 andouter die surface 174.

The coextrusion of elastomeric tubular ply 28 can be accomplished eitherhorizontally, vertically or any angular position therebetween. Samplesof such reinforced elastomeric plies have been successfully coextrudedwherein the diameter of the tubular plies ranged from 2 to about 16inches, the wall thickness ranged from about 0.045 to about 0.125inches, with said tubular plies having end counts ranging from 6 to 48parallel reinforcing elements per circumferential inch, said reinforcingelements being arranged in either curvilinear, i.e., circumferentiallyspaced or staggered arrays.

It should be understood from the previous description that, in terms ofoperation, looking at FIG. 5, for example, one extruder delivers a firstor inner inlet stream of elastomeric stock 206a (FIG. 8), through asingle opening 90 into flow channel 136. The pressure drop from theinlet, at aperture 90, to the furthest outlet, which is 180° angularlyremoved therefrom (via channels 136a, 136b, to first extrudate path 150)must match the resistance in said flow channels, from the inlet to thenearest outlet, since equal pressure is necessary in the 360° expanse ofoutlet stream 206b in order to achieve equal exit velocity. Therefore,the sizings of channel 136 and extrudate path 150 are of primaryimportance in order to achieve the desired matched uniform axialvelocity and mass flow rate in the extrudate.

The same condition exists with reference to the second or outer inletstream 214a of elastomeric stock which enters distribution channel 92through single opening 196, with stream 214a preferably being suppliedby an independent extruder. The pressure and exit velocities of bothoutlet streams 206b and 214b, if of equal thickness, must be the same inorder to achieve a uniform extrudate. While outlet streams 206b and 214bneed not be of the same thickness, their exit velocities must besubstantially matched. Furthermore the inlets 195, 196 for inlet streams206a, and 214a, while preferably coplanar, should be rotated 180° fromanother.

Various known design equations can be used to address the importantmaterial properties of viscosity as well as temperature dependence offlow rate characteristics to determine the appropriate contours, depths,land lengths and land restricted lengths, of channels 92 and 136 as wellas extrudate paths 150 and 200, to obtain the desired uniformity offlows in streams 206b, 214b which will be reasonably insensitive tominor changes of elastomeric stock properties while maintaining desiredtolerances and production capabilities.

As noted, guide means 82 served to precisely direct, locate, space andfeed reinforcing elements 80 into an interface 220 between inner andouter outlet streams 206b, 214b, respectively. Reinforcing elements 80are always located at stream interface 220, but not necessarily centeredbetween streams 206b and 214b. The mass flow ratios of streams 206b and214b must be constant in order to maintain a constant product, but, byvarying one or both of streams 206b, 214b the interface 220 therebetweencan be shifted, thereby changing the radial location of reinforcingelements 80, relative to tubular elastomeric ply 28.

Elastomeric stock outlet streams 206b and 214b have a merging streampressure value of about one-fourth of that at the entrance to their flowchannels 136 and 92, respectively. Nominally, the inlet pressuressupplied to delivery conduits or feed tubes 197, 198 are in the rangesof about 2500-5000 psi. At the merging of streams 206b and 214b, thesepressures drop to a range of about 500-700 psi, while at the exit, fromcoextrusion head 20, the pressures have of course dropped to zero. Whilethe temperature of streams 206 and 214 of elastomeric stock and theirviscous properties influence the pressure values, a minimum pressure isobserved with the balanced and precisely positioned die orifice definedby third extrudate path 204 (FIG. 8).

Streams 206b and 214b have force components which can draw thereinforcing elements 80 into said streams at their interface 220.Therefore, it is possible to replace a broken reinforcing element 80,since, due to the geometry of extrudate paths 150 and 200, there is nolarge pressure gradient that goes back into guide means 82. If onereinforcing element 80 should break, there is only about an one-eighthinch plug of elastomeric stock backflow into guide means 82. This plugcan readily be dislodged in an axially outward direction via a stiff,high modulus object, such as a multifilament steel cord, solid wire, ora rigid plastic monofilament that can be manually inserted into theplugged reinforcing guide means or tube 82 from flared opening 86. Suchan insertion may be accomplished while coextrusion head 20 is inoperation, at low speed, and its operation can be continued with thefull complement of reinforcing elements 80, wherein the high modulusleader being used in front of the desired replacement cord reinforcementelement.

As noted, in order to produce, for example, a 13 inch diameter tubularextrudate having a uniform circumferential wall thickness of about 0.070inches (±0.004 inches), one must be able to assemble, disassemble andoperate coextrusion head 20 within the required tolerances. In order tomaintain this type of precision, one must minimize the number ofindividual components within the coextrusion head. As noted, coextrusionhead 20 is made up of three main elements; namely reinforcing elementguide subassembly 22, inner die assembly 24 and outer die assembly 26.As shown in the several drawings, inner die assembly 24 (FIG. 6) andouter die assembly 26 (FIG. 7) or both, with reference to reinforcingelement guide subassembly 22, can be translated relative to one anotherfor any required servicing, etc. Inner die assembly 24 is provided withland portions 130, 132 for mating and seating relative to guide elementinner wall surface 42, in order to maintain the concentricity betweenguide subassembly 22 and inner die member 24. Furthermore, there is anextremely close tolerance fit between outer wall surface 44 of guidesubassembly 22 and inner surface 168 of outer die inner sleeve 162,again in order to maintain the necessary concentricity between guidesubassembly 22 and outer die assembly 26. If desired, surfaces 44 and168 could also be tapered. Temperature fluid control channels 106 and166 are utilized by the inner and outer die assemblies, respectively inorder to permit heating and cooling of said die assemblies sinceinitially the dies must be heated, but after coextrusion is underwaythey must be cooled in order to maintain the desired operatingtemperatures. Tensioning means, not shown, located externally ofcoextrusion head 20, may take any desired form or shape. A typicalbiased or tensioned reel is shown in FIG. 2 of U.S. Pat. No. 4,484,966to Kawamoto.

As previously explained, a large number of reinforcing elements 80 maybe required, which preferably emanate from individual spools, ribbons orbeams (none shown) in a manner well known in the art. In order tomaintain control of the geometrical shape and gage tolerance of tubularply 28 (FIGS. 8 and 12), ply 28 and each of its reinforcing elements 80must be tensioned, with this tension ranging from about 30 to about 195grams, per individual reinforcing element 80, depending on stocktemperature, viscosity and flow rate, etc.

It has been determined that the difference between the inside diameterof each guide means 82 and the nominal diameter of reinforcing elements80 should be minimal, otherwise there will be excessive backflow of theelastomeric material into guide means 82. Ideally this difference shouldbe about 0.002 inches, but this requires a perfect cord supply, i.e.,one without knots, slubs or splices. Successful operation has beenaccomplished with such perfect cords of 0.028 inch diameter travellingthrough guide tubes of nominally 0.0325 inch inside diameter. Thus, theratio between the nominal diameter of reinforcing elements 80 and theinside diameter of guide means 82 should be less than a factor of 2.

While it is possible to use but one extruder and split the extrudateemanating therefrom, it is easier to control individual separateextruders for producing elastomeric stock inlet streams 206a and 214a.If desired, multiple extruders could be used to produce each of inletstreams 206a and 214a, with these extruders forming successive arcs ofthe required 360° stream distribution. In order to achieve a uniformpressure drop and velocity at the exit of elastomeric body 28, fromcoextrusion head 20, for the full 360°, the pressure drop in bothstreams has to be the same. Computer control is preferably utilized tocontrol the ratio of the two extruder feed rates and speed (rpm)control, together with temperature control. Naturally the rheologicalprediction of the behavior of the elastomeric compositions utilized willinfluence the varying cross sections of channels 92 and 136. Inaddition, the tension on all the reinforcing elements must be uniformand, as can be seen in the several drawings, in order to achieve thesame pressure drop over the entire 360° extent, the effectivelength/diameter ratio of extrudate paths 150 and 200 is varied.Furthermore, it is also possible to shift the radial position of theinterface between the two flow streams by changing the dimensions and/orthe spacing between the inner and outer die assemblies.

Tubular elastomeric ply 28 of the present invention finds utility in amyriad of applications requiring tubular elements--be they tubes, belts,tire bodies, air springs, shock sleeves and the like. For suchapplications, as tubular elastomeric ply 28 emanates from coextrusionhead 20, it is preferably guided and severed circumferentially, in anydesired manner, prior to undergoing further operational shaping,assembly and curing steps. Not only are the reinforcing elements closelypacked, precisely spaced and uniformly surrounded by elastomeric matrixmaterial, but also and very importantly so, because of the tubularconfiguration, there is no splice, no overlap, no out-of-roundness andno static or dynamic force imbalance. X-ray inspections of cured tiresutilizing body plies of the tubular elastomeric components, produced bythe apparatus and method of this invention, reveal a remarkableuniformity of reinforcing element placement.

Tubular elastomeric ply 28 also finds additional utility in terms ofsheets or strips of any desired length that can be produced bylongitudinal severing, such as by splitting or slitting, etc. Suchsevering can be accomplished in any desired manner as, or after, tubularelastomeric ply 28 emanates from coextrusion head 20. The resultingsheets or strips can thereafter be severed or processed into any desiredgeometric configurational shapes or products which are later cured toform mechanical goods for useful industrial and consumer applications.The uniformity of gage and reinforcing element placement of saidresulting sheets or strips, via their production from a tubular ply, isfurther enhanced by the negation of the usual edge effects that areunavoidably present in the production of extruded flat strips, sheets orribbons.

It should be understood that the term elastomeric is deemed to furtherinclude elastoviscous and plastic materials. Furthermore, if desired,the two streams 206 and 214 of elastomeric material that are combined toform the matrix for elastomeric ply 28 may be of differing compositionsand/or thicknesses. In addition, adjacent reinforcing members 80 may beof differing compositions and/or thicknesses, or there may be one ormore staggered or curvilinear arrays of such members. Further yet, whilethe die assemblies of the present invention are preferably configured soas to produce a tubular extrudate, such as a hollow right circularcylinder, said configuration can also include other cylindrical shapeswhose cross sections are other than cylindrical, i.e. oval, for example.

From the foregoing description, and the operational discussion, it isbelieved that those familiar with the art will readily recognize andappreciate the novel concepts and features of the present invention.Obviously, while the invention has been described in relation to only alimited number of embodiments, numerous variations, changes,substitutions and equivalents will present themselves to persons skilledin the art and may be made without necessarily departing from the scopeand principles of this invention. For example, multiple concentriccircular arrays of reinforcing elements could be utilized, as long aseach such array is drawn into the merging interface of two streams ofelastomeric material. As a result, the embodiments described herein aresubject to various modifications, changes and the like without departingfrom the spirit and scope of the invention, with the latter beingdetermined solely by reference to the claims appended hereto.

What is claimed is:
 1. A coextrusion head for producing a generallytubular elastomeric ply made up of first and second coaxial tubularstreams of elastomeric materials having interposed adjacent to theirinterface a closely and uniformly spaced large array of parallel andindependent reinforcing elements, said coextrusion head comprising incombination:(a) a reinforcing element guide subassembly including agenerally annular guide element having an outer wall surface and aninner wall surface as well as axially-directed guide means forindividually and independently directing and accurately positioning acircular array of closely and uniformly spaced individual reinforcingelements; (b) a generally annular inner die assembly, having inner andouter wall surfaces, coaxial with and located substantially radiallyinwardly of said annular guide element, at least one of said annularguide element and said inner die assembly having a 360° annularcontoured channel in the wall surface, opposed to the wall surface ofthe other, said channel together with said opposed wall surface forminga first distribution channel; (c) a generally annular outer dieassembly, having inner and outer wall surfaces, coaxial with and locatedsubstantially radially outwardly of said annular guide element; (d) atleast one of said annular guide and said outer die assembly having a360° annular channel in the wall surface opposed to the wall surface ofthe other, said channel together with said opposed wall surface forminga second distribution channel; (e) the axial outer portions of the innerand outer wall surfaces of said annular guide element having convergingportions merging into an end portion having a narrow annular outer endsurface with said guide means having axial outlet end faces co-planarwith said guide element narrow annular end surface; (f) a portion of theouter wall surface of said inner die assembly and a portion of the innerwall surface of said annular guide element, both axially outward of saidfirst distribution channel, cooperating to form a first generallytubular extrudate path; (g) a portion of the outer wall surface of saidannular guide element and a portion of the inner wall surface of saidouter die assembly,, both axially outward of said second distributionchannel, cooperating to form a second generally tubular extrudate path;(h) the axially outermost portions of the inner wall surface of saidouter die and the outer wall surface of said inner die cooperating toform a third generally tubular extrudate path, said first and secondextrudate paths merging together into said third generally tubularextrudate path at the narrow annular end surface of said guide element;(i) first and second inlet streams of elastomeric materials enter saidfirst and second distribution channels and consequently said first andsecond annular tubular extrudate paths, respectively, and produce saidfirst and second tubular streams which merge together into a combinedthird tubular stream of elastomeric material in said third extrudatepath; (j) said individual reinforcing elements being introduced into theinterface between said first and second streams of tubular elastomericmaterial as they merge together simultaneously with said individuallyand independently guided reinforcing elements into said third tubularstream of elastomeric material thus producing said tubular elastomericply that is internally provided with said closely and uniformly spacedarray of parallel reinforcing elements.
 2. The coextrusion head of claim1 wherein said guide means for individually and independently directingand accurately positioning said reinforcing elements includes at leastone spaced array of adjacent thin walled deformable semi-rigid tubes. 3.The coextrusion head of claim 2 wherein said at least one array of tubesis curvilinear.
 4. The coextrusion head of claim 2 wherein said at leastone array of tubes is staggered.
 5. The coextrusion head of claim 2wherein the inlet portions of said tubes are flared in order to preventchafing of said reinforcing elements.
 6. The coextrusion head of claim 2wherein the ratio of the inside diameter of said tubes, relative to thediameter of said reinforcing elements is less than 2 to
 1. 7. Thecoextrusion head of claim 1 wherein said inner die assembly has said360° annular contoured channel in its outer wall surface, said channel,together with said inner wall surface of said guide subassembly, formingsaid first distribution channel.
 8. The coextrusion head of claim 7wherein said annular guide element is provided with a radially directedaperture and said outer die assembly is provided with opposedradially-directed first and second apertures, said first aperture, whichis aligned with said radially directed aperture in said annular guideelement, is also aligned with a corresponding portion of said first 360°distribution channel.
 9. The coextrusion head of claim 8 wherein saidportion of said first 360° distribution channel, aligned with said firstaperture is provided with an axial central flow divider across saidfirst distribution channel.
 10. The coextrusion head of claim 9 whereinsaid first distribution channel is comprised of two substantiallysimilar and angularly oppositely directed 180° portions of varying crosssection which emanate from said flow divider.
 11. The coextrusion headof claim 1 wherein said guide subassembly has said 360° annularcontoured channel in its outer wall surface, said channel together withthe inner wall surface of said outer die assembly, forming said seconddistribution channel.
 12. The coextrusion head of claim 11 wherein saidouter die assembly is provided with opposed radially-directed first andsecond apertures, said second aperture being aligned with acorresponding portion of said second 360° distribution channel.
 13. Thecoextrusion head of claim 12 wherein said portion of said second 360°distribution channel, aligned with said second aperture, is providedwith an axial central flow divider across said second distributionchannel.
 14. The coextrusion head of claim 13 wherein said seconddistribution channel is comprised of two substantially similar andangularly oppositely directed 180° portions of varying cross sectionwhich emanate from said flow divider.
 15. The coextrusion head of claim12 wherein said radially directed first and second apertures are locatedin a common plane and are 180° removed from one another.
 16. Thecoextrusion head of claim 15 wherein said first and second inlet streamsof elastomeric material enter said extrusion head via said first andsecond radially directed apertures in said outer die assembly.
 17. Thecoextrusion head of claim 1 wherein the axial outer portion of saidannular guide element inner and outer wall surfaces merge into anannular tapered end portion having an included angle ranging from about30° to about 180°.
 18. The coextrusion head of claim 17 wherein saidincluded angle preferably ranges from 100° to 120°.
 19. The coextrusionhead of claim 17 wherein said annular tapered end portion is a solid ofrevolution of generally trapezoidal shape in radial section.
 20. Thecoextrusion head of claim 1 wherein the portion of the outer wallsurface of said inner die assembly, which cooperates with a portion ofsaid inner wall surface of said annular guide element to form said firstextrudate path, and the portion of the inner wall surface of said outerdie assembly, which cooperates with a portion of said outer wall surfaceof said annular guide element to form said second extrudate path,cooperate to define a generally inwardly tapered annular shape having anincluded angle ranging from about 180° to about 40°.
 21. The coextrusionhead of claim 20 wherein said included angle preferably ranges from 130°to 110°.
 22. The coextrusion head assembly of claim 1 wherein saidelement guide subassembly includes a back plate, said inner and outerdie assemblies being rigidly secured to said back plate during theoperation of said coextrusion head.
 23. The coextrusion head assembly ofclaim 1 wherein said element guide subassembly includes a back plate andfirst means, mounted on said back plate and operatively interconnectedwith said inner die assembly, for translating said inner die assemblyand said element guide subassembly relative to one another.
 24. Thecoextrusion head assembly of claim 1 wherein said element guidesubassembly includes a back plate and second means, mounted on said backplate and operatively interconnected with said outer die assembly, fortranslating said outer die assembly and said element guide subassemblyrelative to one another.
 25. The coextrusion head of claim 1 whereinsaid closely spaced array of parallel reinforcing elements issubstantially parallel to the direction of coextrusion.
 26. Thecoextrusion head of claim 1 wherein said tubular ply takes the form of ahollow right circular cylinder.
 27. The coextrusion head of claim 1wherein each of said inner and outer die assemblies is provided withindependent means for temperature control.
 28. A coextrusion head forproducing an elongated elastomeric hollow body made up of first andsecond concentric hollow outlet streams of elastomeric materials havinginterposed adjacent to their interface a closely-spaced array ofparallel reinforcing and independent elements, said coextrusion headcomprising in combination:(a) a reinforcing element guide subassemblyincluding a circumferentially continuous guide element having an outerwall surface and an inner wall surface as well as axially-directed guidemeans for guiding and accurately positioning, in cross section, acircular array of closely-spaced individual reinforcing elements; (b) agenerally circumferentially continuous inner die assembly, having innerand outer wall surfaces, concentric with said guide element, said innerdie assembly having a 360° annular contoured channel in its outer wallsurface, said channel together with the inner wall surface of said guideelement, forming a first distribution channel; (c) a generally annularouter die assembly, having inner and outer wall surfaces, concentricwith said guide element; (d) said guide element having a 360° annularchannel on its outer wall surface, said channel, together with the innerwall surface of said outer die assembly, forming a second distributionchannel; (e) the axial outer portions of the inner and outer wallsurfaces of said guide element having converging portions merging intoan annular tapered end portion having a narrow annular end surface; (f)that portion of the outer wall surface of said inner die assembly andthat portion of the inner wall surface of said guide element, bothaxially outward of said first distribution channel, cooperating to forma first, circumferentially continuous annular tubular, extrudate path;(g) that portion of the outer wall surface of said guide element andthat portion of the inner wall surface of said outer die assembly, bothaxially outward of said second distribution channel, cooperating to forma second, circumferentially continuous annular, extrudate path; (h) theaxially outermost portions of the inner wall surface of said outer dieand the outer wall surface of said inner die cooperating to form athird, circumferentially continuous annular, extrudate path, said firstand second extrudate paths merging together into said third extrudatepath at the narrow annular end surface of said guide element annulartapered end portion, said narrow end surface including the axial outerend surfaces of said means for guiding and positioning said array ofindividual reinforcing elements; (i) first and second inlet streams ofelastomeric materials entering said first and second distributionchannels and consequently said first and second annular extrudate paths,respectively and produce said first and second hollow outlet streamswhich merge together into a combined third hollow stream of elastomericmaterial in said third extrudate path; (j) said individual reinforcingelements being introduced into the interface between said first andsecond hollow streams of elastomeric material as they merge togethersimultaneously with said individually and independently guidedreinforcing elements into said third hollow stream of elastomericmaterial thus producing said elastomeric hollow body that is internallyprovided with said closely-spaced array of parallel reinforcingelements.
 29. The coextrusion head of claim 28 wherein said axiallydirected guide means for directing and positioning includes at least onecircumferentially spaced array of adjacent thin-walled rigid tubes. 30.The coextrusion head of claim 20 wherein the narrow annular end face ofthe annular tapered end portion of said guide element is coplanar withthe axial outer end surfaces of said tubes.
 31. The coextrusion head ofclaim 28 further including means, external of said coextrusion head, forcontrolling the tension of each of said reinforcing elements and saidelastomeric hollow body, said tension being in the range from about 30to about 195 grams for each of said reinforcing elements.
 32. Thecoextrusion head of claim 28 wherein the pressures of said first andsecond hollow outlet streams of elastomeric materials, as they mergeinto said combined third hollow outlet stream is in the range of aboutone fifth to about one fourth of the value of the pressures of saidfirst and second inlet streams as they enter said coextrusion head.